Georg Nikolaus von Nissen

Georg Nikolaus von Nissen (sometimes Nicolaus or Nicolai; January 22, 1761 – March 24, 1826) was a Danish diplomat and music historian. He is remembered as the author of one of the first biographies of Wolfgang Amadeus Mozart, still used today as a scholarly source on the life of this composer.

Nissen was born in Haderslev, Denmark. He completed his schooling in 1781 and became "authorized agent of the General Post Office" in Copenhagen in 1781. In 1792 he became a diplomat in the Danish foreign service. As of 1793, he worked in Vienna as chargé d'affaires.

In 1797, while serving in this post, Nissen first met Mozart's widow Constanze, whose husband had died six years earlier in 1791. He was initially her tenant. The two began living together in September 1798.

Constanze had been through an arduous period following Mozart's death, trying to ward off poverty for herself and her two sons. In this she was successful, obtaining a pension from the Emperor, and making considerable money from concerts of Mozart's music and sale to publishers of his works in manuscript. Nissen came to participate in these labors, taking over much of the work of negotiating with publishers. He also helped care for the children, eventually taking (in Ruth Halliwell's words) "the role of a caring father" in the family.

Nissen and Constanze were married in 1809. The marriage did not produce any children.

In 1812 the couple moved to Copenhagen, where Nissen took up a post as a censor. They dwelt there until 1820, at Lavendelstræde 1, a street where many houses of the period are still preserved.

In 1820, Nissen retired, and the couple moved to Salzburg. Nissen had long been planning a biography of Mozart, and the work began seriously in 1823. Nissen benefited greatly when Mozart's now-elderly older sister Nannerl gave him and Constanze a collection of about 400 Mozart family letters. He worked assiduously to assemble all the biographical material he could, including interviews with still living people who had known the composer.

...
Wikipedia